History of Chemistry

Wed, 06/05/2013 - 13:12 -- sewm02

History of Chemistry

This page provides information about the historical development of models of the atom. Chemistry 1105 students can provide substantive contributions to this page in order to earn Outcome 16. Alternatively, Chem 1105 students can earn this outcome by mastering the multiple choice exam questions associated with Outcome 16.

For each historical person listed below, please add the year or years during which important work was accomplished, a clear statement of their research result (or theoretical contribution) and its significance, and a concise description of the experiment that led to the result. In some cases, an important mathematical equation or formula may also be included.

Each piece of information should be clearly referenced. All reference citations, including web citations, should be complete (as you learned to do with Outcome 42.) If the reference is to a web site, a link should be added to the wiki page that takes the reader directly to the web site. See Help link in left menu bar on this page for wiki editing assistance.

All edits you make to this page are recorded in the page history (see tabs at top of page). You will need to log in (upper left corner of page) with your campus uca and password in order to edit the page.



He is a co-originator of the belief that all matter is made up of various imperishable, indivisible elements which he called "atomos" ("atoma" plural) or "indivisible units". This is where we get the English term "atom". His theory argued that atoms only had several properties which include size, shape, and weight. Other properties, such as color and taste, are the result of interactions between the atoms in our bodies and the atoms of the matter that we are dealing with.

Reference: "Democritus." Wikipedia-The Free Encyclopedia. 2 Oct 2008 <[[1]]>.

He coined the term that eventually became "atom" in 450 BC.

Reference: "Atom." Wikipedia-The Free Ecyclopedia. 2 Oct 2008 <[[2]]>.

Democritus lived to around that age of 90. Having been born in Abdera around 459 BCE this was an exceptionally long life for a man of his times. This could be attributed to both his love of happiness and also to his rational logic that he applied to all things in life. In addition to his early theory of the atom (which was at the time philosophy) Democritus was very involved in other activities, from plays and psychology to government and engineering. He has many wise proverbs that still ring true toady, such as "The hopes of right-thinking men are attainable, but those of the unintelligent are impossible."

Reference: "Democritus" -- History of Psychology 16 Dec 2008 <[[3]]>.

Democritus was a strict determinist that believed everything resulted from natural laws. He followed in the footsteps of Leucippus, who he had a lot in common with and carried on the scientific rationalist psychology of their city. He was an atomist, meaning he tried to explain the world without reasoning. He wanted questions answered with a mechanistic explanation and wanted mechanistic answers. Now, modern scientists have answered the questions in the same way and have led to scientific knowledge of in physics.

Reference: "Democritus" -- Philosophy and science 29 Sep 2012 <htp://en.wikipedia.org/wiki/Democritus>.

Democritus was the first person to use the term "atomos." He named the atom after the Greek word atomos, which mean 'that which can't be split.'

Reference: Kross, Brian. "Questions and Answers - Where Does the Word Atom Come from and Who First Used This Word?" Questions and Answers - Where Does the Word Atom Come from and Who First Used This Word? Jefferson Lab, n.d. Web. 09 Dec. 2013. <http://education.jlab.org/qa/history_01.html>.


John Dalton

John Dalton was born on September 6 1766 and died July 27 1844. He was an English chemist, meteorologist and physicist. His best known work is the development of the atomic theory and his research into colour blindness. Dalton published many papers about his idea on the absorption of gases by water and other liquids. These contained his law of partial pressures now known as Dalton's law. He was also one of the earliest workers in volumetric analysis.

John Dalton enunciated Gay-Lussac's law or Charles's law, published in 1802. In the years following the reading of those essays, Dalton published several papers on similar topics, that on the absorption of gases by water and other liquids (1803). This contained his law of partial pressures now known as Dalton's law.

A study of Dalton's own laboratory notebooks, discovered in the rooms of the Lit & Phil, concluded that so far from Dalton being led by his search for an explanation of the law of multiple proportions to the idea that chemical combination consists in the interaction of atoms of definite and characteristic weight, the idea of atoms arose in his mind as a purely physical concept, forced upon him by study of the physical properties of the atmosphere and other gases.

John Dalton came up with his own Atomic Theory. It had five main points which included: (1) Elements are made of tiny particles called atoms. (2) All atoms of a given atom are identical. (3) The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative weights. (4) Atoms of one element can combine with atoms of another element to form chemical compounds; a given compound always has the same relative numbers of types of atoms. (5) Atoms cannot be created, divided into smaller particles; nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together.

The law of definite proportions states that when elements react, they only combine in definite constant ratios. Regardless of the amount, a pure compound always contains the same elements in the same proportions by mass. The law of multiple proportions states that when one element combines with another to form one compound, the mass ratios of the elements in the compounds are simple whole numbers of each other.

Dalton's law of partial pressure can be stated as Ptotal=P1+P2+P3...Pn. P1, P2, P3, and Pn are known are the partial pressure of the individual gases in the mixture.

Examples of chemical equations that follow Dalton's atomic theory would be as follows:  N2 + 3H2 ==> 2NH3  or  2CO + O2 ==> 6H2O + CO ... The reason that these equations do work with Dalton's law is that they meet all requirments. Not only this but in both equations above, the proportions by mass works with the pure compounds. In the second equation above, each of the elements in this equaton can not be destroyed by law.

Some examples that don't follow Dalton's theory are as follows: CCl4 ==> CH4   or   2H2 + O2 ==> 2H2O + Au ... The reason that these equations do not fit Dalton's law is that in a chemical reaction, atoms can only be arranged. Likewise, the atom of any element can not form into the atom of another element.

references: H. (2014). Practice Using Dalton's Law with This Chemistry Sample Problem. Retrieved September 27, 2016, from http://chemistry.about.com/od/workedchemistryproblems/a/daltons-law-of-p...

reference: Law of Definite Proportions - Law of Multiple Proportions - Concept - Chemistry Video by Brightstorm. (n.d.). Retrieved September 27, 2016, from https://www.brightstorm.com/science/chemistry/matter/law-of-definite-pro...

Reference: "John Dalton." Wikipedia, the free encyclopedia 4 Oct 2008. <http://en.wikipedia.org/wiki/John_Dalton>

"John Dalton." "Wikipedia, the free encyclopedia" 27 Sep 2011. http://en.wikipedia.org/wiki/John_Dalton#Gas_laws



Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on earth were not made of atoms, but of the four elements, earth, wind, fire, and water. He believed all substances were made of small amounts of these four elements of matter. Most people followed Aristotle’s idea, causing Democritus’ idea- which was that all substances on earth where made of small particles called atoms- to be over looked for about 2,000 years! Aristotle's view was finally proven incorrect and his teachings are not present in the modern view of the atom.

Reference: "Aristotle." The-History-of-the-Atom -. N.p., n.d. Web. 20 Sept. 2016. ​​https://the-history-of-the-atom.wikispaces.com/Aristotle


"The Continuous Theory of Matter received wide spread support until the 1800's when John Dalton revived the atom concept to explain certain aspects of chemical reactions.

When? Developed in ~340 BC

What? The Idea that all matter can be divided into smaller and smaller pieces without limit.

Why? Since there was no way to test the theory of Discontinuous Matter, Aristotle argued for the Continuous Theory. Aristotle thought matter was continuous. It wasn't made of indivisible parts so no process of division could exhaust the possibilities of division. There will always be more possible room for division."

Reference: Eddinger, S. (2013, September 2). Aristotle's Theory of Continuous Matter. Retrieved September 19, 2016, from https://prezi.com/ihtqdvhg-vgw/aristotles-theory-of-continuous-matter/

Aristotle believed the four elements were dry, moist, hot, and cold, and that by combining different elements change would occur. He contradicted the beliefs at the time, and believed earth, wind, fire, and air to be simple bodies, not elements. Aristotle believed all elements can change from one form to another. He did not experiment on the elements, but took a more physiological approach to understanding the elements and what they create. Aristotle influenced the chemistry world with 4 simple bodies, and how they produce everything on earth. However, after 2000 years, he was finally proven wrong.

Reference: Four Elements: Aristotle. (n.d.). Retrieved November 29, 2016, from https://web.lemoyne.edu/giunta/ea/ARISTOTLEann.HTML

Dmitri Mendeleev

Dmitri Mendeleev was born in Siberia in 1834 and died in 1907. He began to study science in St. Petersburg and graduated in 1856.
     The reason Mendeleev became the main leader in Chemistry was probably because he not only showed how the elements could be organized, but he used his periodic table to: propose that some elements must have had their atomic weight measured incorrectly because the behavior did not agree with his predicition and also predict the existence of eight new elements and the properties that they would have. Mendeleev discovered periodic law and created one of the first periodic tables. He took the 63 known elements (at the time) and arranged them according to atomic weight. He then wrote the fundamental properties of every element on its own card. He saw that atomic weight was important in some way and he recognized that the behavior of the elements seemed to repeat as their atomic weights increased. By noting this, he arranged them by their similarities of properties. He also was able to use his periodic table to predict the existence and properties of eight other elements. 
When he created his table, he left spaces for elements to be added and predicted future elements. His table did not include any of the Noble Gases we have today because they were not discovered at the time. A guy named Moseley modified and corrected Mendeleev's periodic table many times throughout the years. Mendeleev is also known for studying the thermal expansion of liquids and for studying the nature and origin of petroleum. Element 101 is named Mendelevium in his honor.

"Famous Scientists." (n.d.). Dmitri Mendeleev. Retrieved September 27, 2016, from http://www.famousscientists.org/dmitri-mendeleev/

References: "Who was Dmitri Mendeleev?." Kiwi Web, Chemistry and New Zealand. 1998. 7 Oct 2008 <http://www.chemistry.co.nz/mendeleev.htm>.

"Dmitri Mendeleev." Famous Scientists. famousscientists.org. 1 Sep. 2014. Web. 9/22/2015 

"Dmitri Mendeleev." Famous Scientists. Web. 6 Oct. 2015.  http://www.famousscientists.org/dmitri-mendeleev/

"Dmitri Mendeleev." Retrieved September 23, 2016, from http://www.famousscientists.org/dmitri-mendeleev/



J. J. Thomson

J.J. Thompson was credited for the discovery of electrons in 1897.

Reference: "Electron." Wikipedia-The Free Encyclopedia.2 Oct 2008 <[[4]]>.

Thompson conducted a series of experiments involving cathode rays and cathode ray tubes that led him to his discovery. The three experiments are explained below:

Experiment 1: He constructed a cathode ray tube ending in a pair of cylinders with slits in them. The slits were connected to an electrometer. He found that if the rays were bent so that they could not enter the slits, the electrometer would register a very small charge. Concluded that the negative charge was inseparable from the rays.

Experiment 2: He constructed a cathode ray tube with an almost perfect vacuum and coated one end with phosphorescent paint. He found that rays did indeed bend with the influence of an electric field, and it was in a way that indicated a negative charge.

Experiment 3: He measured the mass to charge ratio of cathode rays by measuring how much they were deflected by magnetic fields and how much energy they carried. Concluded that cathode rays were made of particles and called them "corpuscles." The "corpuscles" came from within the atoms of the electrodes. The "corpuscles" that he discovered are identified with the electron which was proposed by G. Johnstone Stoney.

Reference: "J.J. Thompson." Wikipedia-The Free Encyclopedia. 2 Oct 2008 <[[5]]>.

J.J Thomson proposed the plum-pudding model of the atom following his discovery of the electron. According to the plum-pudding model, the negatively charged electrons were dispersed randomly throughout a positively charged material, much like plums embedded in plum pudding.

Reference:  "Atomic Models - The First Atomic Models." Net Industries. Web. 21 Sept. 2015. http://science.jrank.org/pages/621/Atomic-Models-first-atomic-models.html

In America, since plum pudding is not a common dish, it might be easier to see it as a chocolate chip cookie.  The dough would represent the positive, and the chocolate chips would represent the electrons, as described by the plum pudding model.

Villanueva, John Carl. "Plum Pudding Model." Universe Today. 27 Aug. 2009. Web. 14 Oct. 2015. <http://www.universitytoday.com/38326/plum-pudding-model/>.

Mass to charge ratio

In the 19th century the mass-to-charge ratios of some ions were measured by electrochemical methods. In 1897 the mass-to-charge ratio, [m⁄e], of the electron was first measured by J. J. Thomson. By doing this he showed that the electron—postulated earlier to explain electricity—was in fact a particle with a mass and a charge; and that its mass-to-charge ratio was much smaller than that of the hydrogen ion H+.In 1898 Wilhelm Wien separated ions (canal rays) according to their mass-to-charge ratio with an ion optical device with superimposed electric and magnetic fields (Wien filter). In 1901 Walter Kaufman measured the relativistic mass increase of fast electrons. In 1913, Thomson measured the mass-to-charge ratio of ions with an instrument he called a parabola spectrograph. Today, an instrument that measures the mass-to-charge ratio of charged particles is called a mass spectrometer.


Thomson's experiments and big idea:

Thomson built a cathode ray tube. It was connected to an electrometer, a device for catching and measuring electrical charge. Thomson wanted to see if, by bending the rays with a magnet, he could separate the charge from the rays. As Thomson saw it, the negative charge and the cathode rays must somehow be stuck together: you cannot separate the charge from the rays.

He calculated the ratio of the mass of a particle to its electric charge (m/e). He collected data using a variety of tubes and using different gases.

He later announced: ""we have in the cathode rays matter in a new state, a state in which the subdivision of matter is carried very much further than in the ordinary gaseous state: a state in which all matter... is of one and the same kind; this matter being the substance from which all the chemical elements are built up."

Reference: "Three Experiments and One Big Idea." Three Experiments and One Big Idea. American Institute of Physics, n.d. Web. 08 Dec. 2013. <http://www.aip.org/history/electron/jj1897.htm>.


Ernest Rutherford

Ernest Rutherford was the second son born into a family of twelve children on August 30, 1871. His father, James Rutherford, was a Scottish wheelwright. His mother, Martha Thompson, was an English schoolteacher. Growing up, Ernest’s primary education was received at government institutions. When he turned sixteen, he began his secondary education at Nelson Collegiate School. From here, Ernest received a scholarship and moved on to the University of New Zealand, Wellington where he attended Canterbury College. Rutherford received his M.A. in 1893 with a double major in both Mathematics, and Physical Science. His research in New Zealand was focused on the “magnetic properties of iron exposed to high-frequency oscillations." (Nobel Lectures) His thesis Magnetization of Iron by High-Frequency Discharges included an original experiment. His subsequent paper, Magnetic Viscosity, contained descriptions of a highly accurate highly precise device for measuring time down to the hundred-thousandth of a second. This idea produced in 1896 was well ahead of its time.

The post-graduate continued his research at Canterbury College until he received his B.Sc. in 1894. This same year, Rutherford was awarded another scholarship to attend Trinity College, Cambridge. He then became a research student under J.J. Thompson, a fellow Nobel Prize winner. Rutherford was almost immediately taken under J.J. Thompson’s wing in the laboratory. He then created a detector capable of locating electromagnetic waves. From here, Rutherford began collaborating with Thompson on experiments. Together, they studied how ions acted in gases that were treated with x-rays. In 1897, Rutherford received yet another degree, this one, a B.A. in research from Trinity College.

References: From Nobel Lectures, Chemistry 1901-1921, Elsevier Publishing Company, Amsterdam, 1966 <http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html>

Rutherford began his graduate work by studying the effect of x-rays on various materials. Shortly after the discovery of radioactivity, he turned to the study of the α-particles emitted by uranium metal and its compounds.

Before he could study the effect of α-particles on matter, Rutherford had to develop a way of counting individual α-particles. He found that a screen coated with zinc sulfide emitted a flash of light each time it was hit by an α-particle. Rutherford and his assistant, Hans Geiger, would sit in the dark until his eyes became sensitive enough. They would then try to count the flashes of light given off by the ZnS screen. (It is not surprising that Geiger was motivated to develop the electronic radioactivity counter that carries his name.)

Rutherford found that a narrow beam of α-particles was broadened when it passed through a thin film of mica or metal. He therefore had Geiger measure the angle through which these α-particles were scattered by a thin piece of metal foil. Because it is unusually ductile, gold can be made into a foil that is only 0.00004 cm thick. When this foil was bombarded with α-particles, Geiger found that the scattering was small, on the order of one degree.

These results were consistent with Rutherford's expectations. He knew that the α-particle had a considerable mass and moved quite rapidly. He therefore anticipated that virtually all of the α-particles would be able to penetrate the metal foil, although they would be scattered slightly by collisions with the atoms through which they passed. In other words, Rutherford expected the α-particles to pass through the metal foil the way a rifle bullet would penetrate a bag of sand. Reference: "The Gold Foil Experiment (Ernest Rutherford)" Chem Purdue 22 September 2016  http://chemed.chem.purdue.edu/genchem/history/gold.html


At the suggestion of Hans Geiger, Rutherford had Ernest Marsden experiment to see if alpha particles could be scattered through a large angle. Marsden's results were that very small fraction (around 1 out of 20,000). Assuming that the positive charge and majority of the atom's mass are together in one central area of the atom and account for a small fraction of the atom's volume, and developed an equation predicting that "the number of alpha particles scattered through a given angle should be proportional to the thickness of the foil and the square of the charge of the nucleus, and inversely proportional to the alpha particle velocity raised to the fourth power." Rutherford used this information to develop the current atomic structure model that is still used, disproving the previously-accepted plum-pudding model. 

“Ernest Rutherford.” New Page 2, chemed.chem.purdue.edu/genchem/history/gold.html. Accessed 19 Sept. 2017. http://chemed.chem.purdue.edu/genchem/history/gold.html

Rutherford also estimated the size of the nuclues by carefully measuring the fraction of -particles deflected through large angles, which led him to the conclusion that the radius of the nucleus is at least 10,000 times smaller than the nucleus of the atom. Therefore, the vast majority of the volume of the atom is empty space.  http://chemed.chem.purdue.edu/genchem/history/gold.html 

Rutherford also disproved the plum-pudding model by proposing that the atom is made up of mostly empty space. In this empty space, electrons move in circular orbits around a massive positive charge. Rutherford's empty space model explained the small positively charged nucleus would deflect the few particles that came close. 

Socratic contributors. "Rutherford's gold-foil expeirment." Socratic.org. 2012. 20 Sept. 2017.

Hans Geiger and Ernest Marsden

The Geiger–Marsden experiment(s) (also called the Rutherford gold foil experiment) were a landmark series of experiments by which scientists discovered that every atom contains a nucleus where its positive charge and most of its mass are concentrated. They deduced this by measuring how an alpha particle beam is scattered when it strikes a thin metal foil. The experiments were performed between 1908 and 1913 by Hans Geiger and Ernest Marsden under the direction of Ernest Rutherford at the Physical Laboratories of the University of Manchester.

Wikipedia contributors. "Geiger–Marsden experiment." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 8 Nov. 2016. Web. 8 Nov. 2016.


Hans Geiger best known as the co-inventor of the Geiger counter and for the Geiger-Marsden experiment which discovered the atomic nucleus.

In 1902 Geiger started studying physics and mathematics in University of Erlangen. In 1909, he and Ernest Marsden conducted the famous Geiger-Marsden experiment called the gold foil experiment. Together they created the Geiger counter. In 1911, Geiger and John Mitchell Nuttall discovered the Geiger-Nuttall law (or rule), which led to Rutherford's atomic model. In 1928 Geiger and his student Walther Müller created an improved version of the Geiger counter, the Geiger-Müller counter. http://en.wikipedia.org/wiki/Hans_Geiger

On the other hand, Ernest Marsden, who studied at the University of Manchester under Ernest Rutherford and Hans Geiger,contributed to Ernest Rutherford's work on the structure of the atom. Durning the 1900's, Marsden's work consisted of observing that a tiny fraction of alpha particles fires at a thin gold foil were deflected straight back, in which Rutherford used these results to determine a new structure of the atom. (1) Also, Marsden and Geiger continued their study with alpha particles and later, an 1913, correlated the nuclear charge with the atomic number. (2)

Hans Geiger and Ernest Marsden discovered that the nucleus of an atom accounts for most of the atom's mass, but very little of its size. An atom is mostly empty space with a small, dense nucleus.

Reference: "Ernest Marsden" Chemistry Encyclopedia. 23 September 2011.[6](1)
Reference: "Ernest Marsden" National Library of New Zealand. 23 September 2011[7](2)


Robert Millikan

In 1909, Robert Millikan created an experiment that would allow him to measure an electron's charge. In the experiment, a fine spray of oil was ejected above a pair of metal plates (the top of the two had a small hole). As the mist settled, some of the oil dripped into the hole and in the empty space between the plates. Millikan illuminated these drops with X-rays, withdrawing electrons from molecules in the air; these electrons then attached themselves to the oil, giving the drops an electrical charge. By measuring how fast the drops fell when the metal plates were charged and when they were not, Millikan could determine the charge that each drop possessed. After reviewing his results, Robert found that all of the values he obtained were whole-number multiples of -1.60 × 10-19 C. Since a drop of oil can logically only attach to a whole number of electrons, that value is carried by each electron. Once Millikan had measured the electron's charge, he then found the mass using J. J. Thomson's charge-to-mass ratio. The mass was determined to be 9.09 × 10-28 g. Since this experiment, other scientists have found the more accurate mass of the electron to be 9.109383 × 10-28 g.


James, Brady. Chemistry Matter and Its Changes. 5th Edition. New York: John Wiley & Sons Inc.

Robert Millikan's major discovery was the charge of the electron(see above), but he's discovered several other useful findings towards science and chemistry. He proved that the charge for electrons were constant for all in 1910, shortly after executing the "falling-drop method". In 1912-1915 Millikan tested Einstein's photoelectric equation. He then went on to be the first to make a photoelectric determination of Plank's constant(h). Also in 1920-1923 Robert Millikan's work with hot-spark spectroscopsy of the elements led to an expansion of the ultraviolet spectrum. The new limit extended much farther down than the current known limit. Millikan made several discoveries useful to society. Lastly, his findings on the Brownian movement in gases was a major change to society, since it ended opposition to the atomic and kinetic theories of matter.


"Robert A. Millikan - Biographical". Nobelprize.org. Nobel Media AB 2014. Web. 12 Oct 2016. <http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-b...

Website: http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-b...

 Millikan received the Nobel Prize in 1923 in recognition of two major achievements: measuring the charge of the electron in his famous oil-drop experiment (see “This Month in Physics History,” APS News, August/September 2006), and verifying Einstein's prediction of the relationship between light frequency and electron energy in the photoelectric effect, a phenomenon in which electrons are emitted from matter after the absorption of energy from electromagnetic radiation such as x-rays or visible light.

The prevailing theory in the late 19th century of how charge was produced, held that charge was a type of “strain on the ether,” something that could grow or shrink without restrictions. Faraday’s laws of electrolysis, which were discovered around 1840, provided strong evidence of the quantization of charge, but Faraday never supported the idea. He and most physicists at the time believed that charge, like mass, was an infinitely divisible quantity.

But in 1897, it was realized that cathode rays were in fact tiny charged particles, dubbed “corpuscles” by their discoverer, J. J. Thomson of Cambridge University, and now called electrons. By bending electrons in electric and magnetic fields, investigators could tell that they were negatively charged, and that the ratio of charge to mass, e/m, was the same for all electrons, and about 1700 times larger than that for the ionized hydrogen atom. Thomson believed this was because the charge was the same, but the mass was some 1700 times smaller. Measuring the charge on clouds of water droplets in a cloud chamber, he and his collaborators were able to determine that the charge on the electron, or at least the average charge on the electrons in a cloud, was roughly 10-19 Coulombs (the Coulomb is the unit of charge in the metric system). This was consistent with his hypothesis that the charge on the electron was the same as that found in hydrogen. In 1906, Millikan began experiments at the University of Chicago to attempt to measure individual electron charges, and with much greater accuracy than Thomson and co-workers had been able to achieve. One of the great improvements was the use of oil drops instead of the cloud of water drops that Thomson used. In Millikan’s apparatus, the water drops would have quickly evaporated, whereas individual oil drops could be studied for a long time. Millikan’s student Harvey Fletcher played an important role in implementing this improvement.

Millikan set up a pair of parallel conducting plates horizontally, one above the other, with a large electric field between them that could be adjusted. A fine mist of oil was sprayed into a chamber above the plates. Many of the droplets would become negatively charged as they picked up some small, unknown number of electrons as they passed through the nozzle. Some of the drops then fell through a hole in the top plate and drifted into the region between the two parallel plates. Lit from the side by an intense light, these drops glistened when the region was viewed through a microscope.

With the electric field turned off, Millikan could observe a falling drop and measure its terminal velocity. This measurement gave him the radius of the drop, and since he knew the density, he could determine the mass. He could then switch on the electric field, and adjust it so that the electric force just precisely balanced the force of gravity on the drop. Knowing the strength of the field and the mass of the drop, he could calculate the only unknown, the charge on the drop. This measurement was repeated many times, and often the same drop would be allowed to rise and fall in the apparatus again and again, as it picked up and shed electrons.

Working with Fletcher, Millikan showed that the charge of the droplets were always a whole number multiple of 1.592 x10-19C, the basic unit of charge. Today, the accepted value is 1.602x10-19C. He published his results in 1913.



There are many possible examples of the droplet charge. These charges help to indicate how many extra electrons the droplet has. For example, 3.2*10^-19 is the charge of a droplet with two extra electrons, and something like 8.0*10^-19 is the charge of a droplet with 5 extra electrons.

Reference: https://www.ck12.org/book/CK-12-Physics-Concepts-Intermediate/section/17.3/

Neils Bohr

Neil Bohr first started experiments under J.J. Thomson and he later went to study under Ernest Rutherford. After studying and experimenting with Rutherford, Neil Bohr published his model of atomic structure in 1913 which introduced the theory of electrons traveling in orbits around the atom's nucleus and the chemical properties of the element being largely determined by the number of electrons in the outer orbits. Neil Bohr also introduced the idea that an electron could drop from a higher-energy orbit down to a lower energy-orbit, emitting a photon of discrete energy. This idea became the basis of the quantum theory.

Neil Bohr contributed to chemistry and physics in the following ways: Bohr's model-the theory that electrons travel in discrete orbits around the atom's nucleus, the shell model of atom-where the chemical properties of an element are determined by the electrons in the outermost orbit, the correspondence principle-the basic tool of the old quantum theory, the liquid drop model of the atomic nucleus, identified the isotope of uranium that was responsible for slow-neutron fission, much work on the Copenhagen interpretation of quantum mechanics, and the principle of complementary-that items could be separately analyzed as having several contradictory properties.

Reference: http://en.wikipedia.org/wiki/Neils_Bohr

Bohr also conceived the principle of complementarity: that items could be separately analyzed as having several contradictory properties. For example, physicists currently conclude that light behaves either as a wave or a stream of particles depending on the experimental framework — two apparently mutually exclusive properties — on the basis of this principle. reference: http://en.wikipedia.org/wiki/Niels_Bohr

The Bohr model, devised by Niels Bohr, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. This was an improvement on the earlier cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911). Since the Bohr model is a quantum physics-based modification of the Rutherford model, many sources combine the two, referring to the Rutherford–Bohr model. reference: http://en.wikipedia.org/wiki/Bohr_model

Niels Bohr's model of an atom had six different assumptions (1) The electron travels around the nucleus in a circular orbit. (2) The energy of the electron in orbit is proportional to its distance from the nucleus. (3) Only a limited number of orbits with certain energies are allowed. (4) The only orbits that are allowed are those for which the angular momentum of the electron is a multiple of Plank's constant divided by 2. (5) Light is absorbed when an electron jumps to a higher energy orbit an demitted when an electron falls into a lower energy orbit. (6) The energy of the light emitted or absorbed is exactly equal to the difference between the energies of the orbits. Reference: http://chemed.chem.purdue.edu/genchem/history/bohr.html

James Chadwick

James Chadwick was born in Bollington, Cheshire, the son of John Joseph Chadwick and Anne Mary Knowles. He went to Bollington Cross C of E Primary School, attended Manchester High School, and studied at the Universities of Manchester and Cambridge. In 1913 Chadwick went and worked with Hans Geiger at the Technical University of Berlin. He also worked with Ernest Rutherford. He was in Germany at the start of World War I and would be interned in Ruhleben P.O.W. Camp just outside Berlin. During his internment he had the freedom to set up a laboratory in the stables. With the help of Charles Ellis he worked on the ionization of phosphorus and also on the photo-chemical reaction of carbon monoxide and chlorine. He spent most of the war years in Ruhleben until Geiger's laboratory interceded for his release.

In 1932 Chadwick made a fundamental discovery in the domain of nuclear science: he discovered the particle in the nucleus of an atom that became known as the neutron because it has no electric charge. In contrast with the helium nuclei (alpha particles) which are positively charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any Coulomb barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements. In this way, Chadwick prepared the way towards the fission of uranium 235. For this important discovery he was awarded the Hughes Medal of the Royal Society in 1932, and subsequently the Nobel Prize for Physics in 1935.

Chadwick’s discovery made it possible to create elements heavier than uranium in the laboratory. His discovery particularly inspired Enrico Fermi, Italian physicist and Nobel laureate, to discover nuclear reactions brought by slowed neutrons, and led Otto Hahn and Fritz Strassmann, German radiochemists in Berlin, to the revolutionary discovery of “nuclear fission”.

Chadwick became professor of physics at Liverpool University in 1935. As a result of the Frisch-Peierls memorandum in 1940 on the feasibility of an atomic bomb, he was appointed to the MAUD Committee that investigated the matter further. He visited North America as part of the Tizard Mission in 1940 to collaborate with the Americans and Canadians on nuclear research. Returning to England in November 1940, he concluded that nothing would emerge from this research until after the war. In December 1940 Franz Simon, who had been commissioned by MAUD, reported that it was possible to separate the isotope uranium-235. Simon's report included cost estimates and technical specifications for a large uranium enrichment plant. James Chadwick later wrote that it was at that time that he "realized that a nuclear bomb was not only possible, it was inevitable. I had then to take sleeping pills. It was the only remedy."

He shortly afterward joined the Manhattan Project in the United States, which developed the atomic bombs dropped on Hiroshima and Nagasaki. Chadwick was knighted in 1945.

Source of Material: http://en.wikipedia.org/wiki/James_Chadwick


Wolfgang Pauli

Wolfgang Pauli was outstanding among the brilliant mid century school of physicists. He was recognized as one of the leaders when, barley out of his teens and still a student, he published a mastery exposition of the theory of relativity. His exclusion principle, which is often quoted bearing his name, crystallized the existing knowledge of atomic structure and it led to the recognition of the two valued variable required to characterize the state of an electron. Pauli was the first to recognize the existence of the neutrino, an uncharged and massless particle which carries off energy in radioactive B-disintegration. [4] 

Wolfgang Pauli received the Nobel Prize in physics in 1945, for the discovery of the exclusion principle, also called the Pauli Principle. The principle was proposed in 1925 as an assertion that no two electrons in an atom can be at the same time in the state or configuration. This was to account for the observed patterns of light emission from atoms. The exclusion principle subsequently has been generalized to include the whole class of particles called fermions. The Pauli exclusion principle indicates, that only two electrons are allowed in each atomic energy state, leading to the successive buildup of orbitals around the nucleus. This prevents matter from collapsing to an extremely dense state.

Before Pauli's suggested explanation, it was believed that there were only 3 quantum numbers. In late 1924, he suggested adding a fourth quantum number. The first three quantum numbers made sense physically, since they related to the electron's motion around the nucleus, a property which the new quantum number did not fit. Pauli called his new quantum property of the electron a, "two-valuedness not describable classically." This proposed fourth quantum number puzzled physicists at the time because no one could explain its physical significance. Even Pauli himself was trouble by the idea, and also that he couldn't give any logical explanation for the exclusion principle or derive it from other laws of quantum mechanics, and he remained unhappy about this problem. Nonetheless, the principle worked–it explained the structure of the periodic table and is essential for explaining other properties of matter.​


1.Gavryushin,& Zukauskas, "Pauli Exclusion Principle." (18 Apr 2002 ). 23 Oct 2008.

2. Massimi, Michela (2005). Pauli's Exclusion Principle. Cambridge University Press. ISBN 0-521-83911-4.

3. Tretkoff, Ernie. "This Month is Physics History. January 1925: Wolfgang Pauli announces the exclusion principle." Ed. Alan Chodos. American Physical Society. Web. 6 Oct. 2015. http://www.aps.org/publications/apsnews/200701/history.cfm

4. Wolfgang Pauli- Biographical.(n.d.). Retreived October 11, 2016 from http://www.nobelprize.org/nobel_prizes/physics/laureates/1945/pauli-bio.html

Albert Einstein

Albert Einstein is known for his theory of relativity and mass–energy equivalence, E = mc².

Einstein has contributed to physics by his special theory of relativity, his general theory of relativity, and a new theory of gravitation. He also contributed to the advances in the fields of relativistic cosmology, capillary action, critical opalescence, classical problems of statistical mechanics and to quantum theory.

Einstein published over 300 scientific works and over 150 non-scientific works. http://en.wikipedia.org/wiki/Albert_Enstein

After Einstein was finished with his theory of relativity his research consisted of attempts to generalize his theory of gravitation. This is because he wanted to unify and simplify the fundamental laws of physics, in particular, gravitation and electromagnetism.

He described the unified field theory in 1950; however, he was never able to successfully unify the laws of physics under a single model. Because Einstein focused his later work on this unsuccessful model, he ignored the mainstream developments within his field that many people believed he could have clarified.

"Albert Einstein." Wikipedia-the Free Encyclopedia. 17 Dec 2008 [[8]].

Einstein attended school at the Luitpold Gymnasium in Munich. When he moved to Italy, he continued his schooling at Aarau, Switzerland. Einstein was trained as a physics and mathematics teacher at the Swiss Federal Polytechnic School in Zurich. He obtained his diploma in 1901, and he finished his doctorate degree in 1905. Einstein’s special theory of relativity came from his attempt to join the laws of mechanics with the laws of the electromagnetic field. His study of the problems with statistical mechanics and the problems of how they merged with the quantum theory is what led to his explanation of the Brownian movement of molecules. Einstein’s observations of thermal properties of light with low radiation density are what laid the foundation for the photon theory of light. Although Einstein is thought of as only a man of science, he was also active in politics. After WWII, he was a leading figure in the World Government Movement and he was also offered the presidency of Israel. Einstein’s works were recognized with awards such as the Copley Medal of the Royal Society of London, and the Franklin Medal of the Franklin Institute.

"Albert Einstein - Biographical." Nobelprize.org. Nobel Media AB 2013. Web. 29 Sep 2013. <http://www.nobelprize.org/nobel_prizes/physics/laureates/1921/einstein-bio.html>

Erwin Schrodinger

Erwin Rudolf Josef Alexander Schrödinger (12 August 1887 – 4 January 1961) was an Austrian physicist who achieved fame for his contributions to quantum mechanics, especially the Schrödinger equation, for which he received the Nobel Prize in 1933. In 1935, after extensive correspondence with personal friend Albert Einstein, he proposed the Schrödinger's cat thought experiment.

He became the assistant to Max Wien, in Jena, and in September 1920 he attained the position of ao. Prof. (Ausserordentlicher Professor), roughly equivalent to Reader (UK) or associate professor (US), in Stuttgart. In 1921, he became o. Prof. (Ordentlicher Professor, i.e. full professor), in Breslau (now Wrocław, Poland). In 1921, he moved to the University of Zürich. In January 1926, Schrödinger published in the Annalen der Physik the paper "Quantisierung als Eigenwertproblem" [tr. Quantisation as an Eigenvalue Problem] on wave mechanics and what is now known as the Schrödinger equation. In this paper he gave a "derivation" of the wave equation for time independent systems, and showed that it gave the correct energy eigenvalues for the hydrogen-like atom. This paper has been universally celebrated as one of the most important achievements of the twentieth century, and created a revolution in quantum mechanics, and indeed of all physics and chemistry. A second paper was submitted just four weeks later that solved the quantum harmonic oscillator, the rigid rotor and the diatomic molecule, and gives a new derivation of the Schrödinger equation. A third paper in May showed the equivalence of his approach to that of Heisenberg and gave the treatment of the Stark effect. A fourth paper in this most remarkable series showed how to treat problems in which the system changes with time, as in scattering problems. These papers were the central achievement of his career and were at once recognized as having great significance by the physics community.

In 1927, he succeeded Max Planck at the Friedrich Wilhelm University in Berlin. In 1933, however, Schrödinger decided to leave Germany; he disliked the Nazis' anti-semitism. He became a Fellow of Magdalen College at the University of Oxford. Soon after he arrived, he received the Nobel Prize together with Paul Adrien Maurice Dirac. His position at Oxford did not work out; his unconventional personal life (Schrödinger lived with two women) was not met with acceptance. In 1934, Schrödinger lectured at Princeton University; he was offered a permanent position there, but did not accept it. Again, his wish to set up house with his wife and his mistress may have posed a problem. He had the prospect of a position at the University of Edinburgh but visa delays occurred, and in the end he took up a position at the University of Graz in Austria in 1936.

In the midst of these tenure issues in 1935, after extensive correspondence with personal friend Albert Einstein, he proposed the Schrödinger's cat thought experiment


Source of Material- http://en.wikipedia.org/wiki/Erwin_Schrodinger


Louis de Broglie

In 1924, his doctoral thesis in the Research on Quantum Theory introduced the theory of electron waves. This research included the wave-particle duality theory of matter. This theory showed the de Broglie hypothesis, which stated that any moving particle or object had an associated wave. He based this work off of the work of Albert Einstein and Planck. From this research, he created a new branch of physics called wave mechanics. This branch combined the physics of light and matter. Also in the application of his work, he further developed the use of electron microscopes to get much better resolution than optical ones. The reason for this was because of the shorter wavelengths of electrons compared with photon.

Throughout Broglie's life he published numerous articles on varying science topics, as well as taught and mentored students at he institute Henri Poincare in Paris. He received many medals including the Henri Poincare medal in 1929 and the Albert l of Monaco prize in 1932.
Louis de Broglie contributions to chemistry:

-came up with Broglie hypothesis in the wave-particle duality theory

-stated any moving particle or object had an associated wave

-created a new branch of chemistry consisting of the physics of light and matter--called wave mechanics

-further developed use of electron microscope


References: “Louis de Broglie.” Wikipedia, the free encyclopedia. 17 Nov 2008. <http://en.wikipedia.org/wiki/Louis_de_Broglie?>

Louis de Broglie- Biographical.(n.d.).Retreived October 11, 2016 from http://www.nobelprize.org/nobel_prizes/physics/laureates/broglie-bio.html


Max Planck

Max Planck was born on April 23, 1858 in Kiel, Germany. He studied at the Universities of Munich and Berlin, and received his doctorate in philosophy at Munich in 1879. He started his work on thermodynamics which he published papers on. Around 1894, he had an interest on the problems of radiation processes. He was led to the problem of the distribution of the energy in the spectrum of full radiation. He observed wavelength distribution and the energy emitted by a black body to deduce the relationship between the energy and the frequency of radiation. In 1990 he announced that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency v is hv where h is a universal constant, now called Planck's constant. His original constant number was quoted as (6.55×10−27 erg·sec);however, as of March 3, 2014, it is best defined as (6.62606957×10−34 J·s). Planck's work on quantum theory was published in the Annalen der Physik. He also won the Society's Copley Medal in 1928. He died on October 4, 1947 in Göttingen.


Max Planck:The Nobel Prize in Physics 1918. The Nobel Foundation. 13 October 2008. http://nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.html


Johannes Balmer

He was born May 1, 1825, Lausanne, Switz. He died March 12, 1898. During his schooling he excelled in mathematics, and so decided to focus on that field when he attended university. He studied at the University of Karlsruhe and the University of Berlin, then completed his Ph.D. from the University of Basel in 1849. Despite being a mathematician, he is not remembered for any work in that field; rather, his major contribution (made at the age of sixty, in 1885) was an empirical formula for the visible spectral lines of the hydrogen atom. Using Ångström's measurements of the hydrogen lines, he arrived at a formula for finding the wavelength as follows:


for n = 2, h = 3.6456×10−7 m, and m = 3, 4, 5, 6, and so forth. In his 1885 journal he referred to "h" as the "fundamental number of hydrogen." His formula was later revised by Johannes Rydberg as finding the frequency of a wavelength.

Reference: Balmer, Johannes. Wikipedia The Free Encyclopedia. 23 Sept. 2008. Date accessed 3 Dec. 2008. http://en.wikipedia.org/wiki/Johann_Jakob_Balmer

Johann Jakob Balmer discovered a formula basic to the development of atomic theory and the field of atomic spectroscopy. The atomic theory is a scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms. Spectroscopy is the study of the interaction between matter and electromagnetic radiation. In 1885 he announced a simple formula representing the wavelengths of the spectral lines of hydrogen—the “Balmer series”. The Balmer Series is a series of spectral emission lines of the hydrogen atom that result from electron transitions from higher levels down to the energy level with principal quantum number 2.

The Balmer equation could be used to find the wavelength of the absorption/emission lines and was originally presented as \lambda \ =B\left({\frac  {n^{2}}{n^{2}-m^{2}}}\right)=B\left({\frac  {n^{2}}{n^{2}-2^{2}}}\right).


λ is the wavelength.

B is a constant with the value of 3.6450682×10−7 m or 364.50682 nm.

m is equal to 2

n is an integer such that n > m.

Why the formula held true, however, was not explained until 1913, when Niels Bohr  found that it fit into and supported his theory of discrete energy states within the hydrogen atom. 





Johannes Rydberg

Johannes Robert Rydberg was a Swedish physicist mainly known for devising the Rydberg formula, in 1888, which is used to predict the wavelengths of photons (of light and other electromagnetic radiation) emitted by changes in the energy level of an electron in an atom.

The physical constant known as the Rydberg constant is named after him, as is the Rydberg unit. Excited atoms with very high values of the principal quantum number, represented by n in the Rydberg formula, are called Rydberg atoms, and a crater on the moon is also named Rydberg in his honour. Rydberg's faith that spectral studies could assist in a theoretical understanding of the atom and its chemical properties was justified in 1913 by the work of Niels Bohr (see hydrogen spectrum). An important spectroscopic constant based on a hypothetical atom of infinite mass is called the Rydberg (R) in his honor.

Source of Material - http://en.wikipedia.org/wiki/Johannes_Rydberg

By examining all the lines in the spectrum of the hydrogen atoms, an empirical model was derived that explained the pattern of the emission. The specific wavelengths (or frequencies or energies) could be predicted based upon a constant and two integers. The interpretation was that one integer represented the initial state and one integer the final state. The wavelength (or frequency or energy) was related to the change that occurred moving between these two states.

The original formula related inverse wavelength (known as "wavenumber") to the integers that were related to the initial and final states. 1λ=R(1/nf^2−1/ni^2) where R is equal to 1.097×10^7 m^-1 and nf and ni  are integers that describe the initial and final states of the electron.

While the original formula derived by Rydberg did not look directly at energies, we can rewrite the formula to have these units. Under these conditions, the change in energy of the electron is given by ΔE=R(1/nf^2−1/ni^2). Now the constant R (the Rydberg constant) is equal to 2.178×10^−18 J.

Source Website- http://ch301.cm.utexas.edu/section2.php?target=atomic/H-atom/rydberg.html

Rydberg decided to use the wave number as a measure of frequency in his calculations. A wave number is the reciprocal of wavelength. What Rydberg did not know at the time was that it was directly related to energy. With the change, patterns began to emerge in the data with a particular series of lines for any atom leading to a hyperbolic relationship.

Source Material:


C. Davisson and L. H. Germer; G. P. Thomson

>p Three years after de Broglie asserted that particles of matter could possess wavelike properties, the diffraction of electrons from the surface of a solid crystal was experimentally observed by C. J. Davisson and L. H. Germer of the Bell Telephone Laboratory. In 1927 they reported their investigation of the angular distribution of electrons scattered from nickel. With careful analysis, they showed that the electron beam was scattered by the surface atoms on the nickel at the exact angles predicted for the diffraction of x-rays according to Bragg's formula, with a wavelength given by the de Broglie equation, λ = h / mv. Also in 1927, G. P. Thomson, the son of J. J. Thomson, reported his experiments, in which a beam of energetic electrons was diffracted by a thin foil. Thomson found patterns that resembled the x-ray patterns made with powdered (polycrystalline) samples. This kind of diffraction, by many randomly oriented crystalline grains, produces rings. If the wavelength of the electrons is changed by changing their incident energy, the diameters of the diffraction rings change proportionally, as expected from Bragg's equation.


1.Colwell, Catherine H.. "Famous Experiments: Davisson-Germer." Physics Lab. 2008. 23 Oct 2008 <http://dev.physicslab.org/Document.aspx?doctype=3&filename=AtomicNuclear_DavissonGermer.xml>.


Werner Heisenberg

In 1925, Heinsenberg, with mathematical help from Max Born, developed the first version of quantum mechanics, a matrix method of calculating the behavior of electrons and other subatomic particles.The method was superseded as a practical tool soon after by the more intuitive wave equation of Erwin Schrodinger, but the matrix mechanics remains a great intellectual accomplishment.In 1927, the German physicist Werner Heisenberg showed mathematically that it is impossible to measure with complete precision both a particle's velocity and position at the same instant. To measure an electron's position or velocity, we have to bounce another particle off it. Thus, the very act of making the measurement changes the electron's position and velocity. We can not determine both exact position and exact velocity simultaneously, no matter how cleverly we make the measurements. This was Heisenberg's famous uncertainty principle. The theoretical limitations on measuring speed and position are not significant for large objects. For small particles such as the electron, however, these limitations prevent us from ever knowing or predicting where in an atom an electron will be at a particular instant, so we speak of probabilities instead.A few years later he introduced a new quantum number called isotopic spin, which is a quantum-mechanical variable, resembling the angular momentum vector in algebraic structure whose third component distinguished between members of groups of elementary particles. He continued to contribute to particle physics, introducing useful computational techniques in the 1950s.

Consequently, wave mechanics describes the probable locations of electrons in atoms. Wave mechanics views the probability of finding an electron at a given point in space as equal to the square of the amplitude of the electron wave at that point. In each orbital the electron is conveniently viewed as an electron cloud with a varying electron density.


1. James, Brady. Chemistry Matter and Its Changes. 5th Edition. New York: John Wiley & Sons Inc.

2. "Werner Karl Heisenberg." Answers.com. 2008. Answers Corporation. 23 Oct 2008 <http://www.answers.com/topic/werner-heisenberg>.



Fritz Wolfgang London, a theoretical physicist, was born Breslau, Silesia, Germany in 1900. He had a position at the University of Berlin, but lost it due to Hitler's Nazi Party Racial laws in 1933. He took positions in England and in France, then later emigrated to the United States in 1939, where he became a professor at Duke University. With his brother Heinz, he made fundamental contributions to the theories of chemical bonding and intermolecular forces. London also worked with Walter Heilter on chemical bonding and is now in the textbooks as we know today. His work with Heitler was the first to completely explain the bonding in a homonuclear molecule as H2.

London's early work was in the area of intermolecular forces. He observed the attraction between two rare gas atoms at a large distance from each other. This attraction is now known as "London Force". 

For atoms and nonpolar molecules, the London dispersion force is the only intermolecular force and is the reason that they exist in solid and liquid states. For polar molecules, the London dispersion force is one part of the van der Waals force as well as the permanent molecular dipole moments.

Source of Material: http://en.wikipedia.org/wiki/Fritz_London

The London Dispersion Forces, named after Fritz London, exist between atoms. They become stronger when dealing with larger atoms, more surface contact between molecules, and larger electron clouds.LDF is a weak intermolecular force that is part of the Van der Waals Force.

LDF exists when electrons try to avoid each other. These forces are exhibited by nonpolar molecules because of the movements of the electrons within the molecules. These forces allow noble gasses to be found in a liquid form because they would otherwise have no attractive forces, and would not conjeal together. Although it may seem odd, these forces are weaker than ionic bonds, and even hydrogen bonds.

Source of Material: http://en.wikipedia.org/wiki/London_dispersion_force



- Hess's law is a law of physical chemistry created by Germain Hess.It is the expansion of the Hess Cycle and used to predict the enthalpy change and conservation of energy regardless of the path through which it is to be determined.

- Hess's law states that because enthalpy is a state function, the enthalpy change of a reaction is the same regardless of what pathway is taken to achieve the products.

- Hess's law has also led to an extension to entropy and free energy. For example the Bordwell thermodynamic cycle takes advantage of easily measured equilibrium and redox potentials to determine experimentally inaccessible Gibbs free energy values.

- The law states that the energy change for any chemical or physical process is independent of the pathway or number of steps required to complete the process. In other words, an energy change is path independent, only the initial and final states being of importance.

Citation: "Hess's law." Wikipedia-the free encyclopedia.3 Dec. 2008. [[9]].

---An illustration of Hess's law which would be incorporated in thermal chemical equations

  • A+B=AB, dH1
  • AB+B=AB2,dH​1 2
  • So the following is true A+2B=AB2dH​​1 2=dH1+dH

Citation: Chung Chieh"Hess's Law." CAcT-Computer Assisted Chemistry Tutor. 15 Oct. 2015 [http://www.science.uwaterloo.ca/~cchieh/cact/c120/hess.html]

Theodore W Richards

Theodore W. Richards was born in Germantown, Pennsylvania in 1868. When Theodore was only 10 years old, his family moved to Europe for a few years, which greatly influenced his interest in science. Upon returning to the United States, he entered Haverford College at age 14, and eventually graduated from Harvard. He received his PhD in chemistry and began his research by working with oxygen and copper and eventually, developed a new way to determine atomic weights. By 1912, he had determined over 30 atomic weights, with the highest degree of accuracy. At the end of his chemistry career, he and his students had discovered over 55 atomic weights that are still used today. He played a large part in modernizing the concept of an atom. He also did research on atomic and molecular volume. Richards was responsible for introducing the use of transition temperatures and using hydrated salts as fixed points in standard thermometers. However, his biggest achievement was becoming the first American scientist to win the Nobel Prize in Chemistry in 1914. Today, there is an award known as the Theodore William Richards Medal for Conspicuous Achievement in Chemistry and the Theodore William Richards Medal.


- "Theodore W. Richards." Nobel Lectures. The Nobel Foundation. 9 Dec 2008 <http://nobelprize.org/nobel_prizes/chemistry/laureates/1914/richards-bio.html>.

-"Theodore W. Richards." Wikipedia, the free encyclopedia. 16 Sept 2008. 11 Dec 2008 <http://en.wikipedia.org/wiki/Theodore_William_Richards>.

-"The Theodore William Richards Medal." The Northeastern Section of the American Chemical Society. 2008. 11 Dec 2008 <http://www.nesacs.org>.




Eugen Goldstein

Eugen Goldstein was a German physicist that was born in Gliwice, Poland in 1850. He went on to study at the University of Wroclaw and did his research at the Berlin Observatory. His work dealt with the vacuum ray tubes. He coined the term "cathode rays" for the negatively charged ions that passed through the vacuum ray tubes.

Although he was not credited with the discovery of the proton, Eugen Goldstein had many contributions that lead to further discoveries related to subatomic particles.

In 1886, Goldstein discovered anode rays, or the positively charged particles that went through the vacuum tubes when the electrons were removed. When a magnetic field was introduced to the vacuum tube it would bend the pattern of the ray. This distortion of the ray would suggest that it was made up of positively charged ions. In this way, Eugen Goldstein had discovered the proton without even knowing it.


Citation: Soylent Communications (2014) "Eugen Goldstein" Retrieved Sept. 20 from: http://www.nndb.com/people/887/000169380/


Submitted by mconti on

In the seventh subtitle, Robert's Last name is misspelled. His last name should be written as in the "Millikan," not "Millilkan."

Submitted by mconti on

 As I was reading for the charge-to-mass ratio of electrons, I noticed that J.J. Thomson's last name was also misspelled. In the subtitle, it was written as "Thompson". 

Submitted by mstrait1 on

Henry Moseley was a visionary who worked with physics and worked on theories that then continued to change how people approached atoms and molecules. Moseley's contributions had a huge affect of modern science.

Henry Moseley's most important work was the acceptance of "Moseley's Law" which proved that the atomic number of the element is actually equivalent to the charge inside the nucleus of an atom.

Henry Moseley decided to join the British Army during World War 1, however he was killed in August of 1915. Moseley won the "Matteucci Medal" in 1919 for his contributions to physics and chemistry.

Reference: "Henry Moseley Biography." - Childhood, Life Achievements & Timeline. Web. 6 Oct. 2015. <http://www.thefamouspeople.com/profiles/henry-moseley-6556.php>.


Submitted by mmetzger1 on

Theodore W. Richards also provided experimental verification of the isotope concept, showing that lead from different sources has different atomic weights. He analyzed samples of naturally occurring lead and lead produced by radioactive decay. His measurements showed that the two samples of lead had different atomic weights. 


"Theodore William Richards." Chemical Heritage Foundation. Chemical Heritage Foundation, 30 Sept. 2015. Web. 18 Sept. 2016. https://www.chemheritage.org/historical-profile/theodore-william-richards

"Theodore William Richards." Wikipedia. Wikimedia Foundation, n.d. Web. 18 Sept. 2016. <https://en.wikipedia.org/wiki/Theodore_William_Richards>.

Submitted by ccutlip5 on

     Marie Curie was born in Warsaw, Poland on November 7th 1867. Marie Curie and her husband, Pierre, were influential in the isolation and discovery of Polonium and Radium. These elements are used in many things that other elements are not capable of doing. For polonium, this involves being a part of brushes used in the development of film, and on space satellites as a heat resistant element. In both of these cases, the polonium is sealed as to prevent radiation from leaking and causing harm. Radium is used to obtain Radon gas, which is used to treat cancer patients. 


     Marie Curie truly believed that her science could help others. She was one of few women in that time and moved around in order to achieve the best possible education. While experimenting in her free time, both Pierre and Marie Curie taught as a way to generate an income. Her and her husbands findings were proved beyond a doubt when she was able to isolate the metal of radium, giving irrefutable proof that her data was legitimate. When World War 1 rolled in, Marie actively promoted the use of Radium to better treat and heal soldiers. She was awarded the Nobel prize for Physics in 1903, and eventually surcame to illness as a result of her years of unprotected contact with radioactive elements.

Submitted by ipringle on

Theodore Richards developed a new technique for determining halide ratios. He invented the nephelometer and demonstrated insidious effect of occluded moisture in gases and solids. He also invented the adiabatic calorimeter which helped determine the atomic compressibility’s and volumes. To accurately measure atomic weights consistently of more than thirty elements, he found the atomic compressibility and volumes and compared it to the atomic weights as shown below.


Herschbach, D. R. (2014). Theodore William Richards: Apostle of Atomic Weights and Nobel Prize Winner. Retrieved September 19, 2017, from https://faculty.chemistry.harvard.edu/files/dudley-herschbach/files/trw2014-angchem.pdf .